Update cmark to https://github.com/github/cmark/commit/a457ab287d14834d43025541f3bc9f4751de6872
Update cmark to https://github.com/github/cmark/commit/a457ab287d14834d43025541f3bc9f4751de6872

gjtorikian/commonmarker,gjtorikian/commonmarker,gjtorikian/commonmarker